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Tools to assist in the reading of configuration/preferences files in
various formats
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.configuration2.builder.combined;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicReference;
import org.apache.commons.configuration2.ConfigurationUtils;
import org.apache.commons.configuration2.FileBasedConfiguration;
import org.apache.commons.configuration2.builder.BasicBuilderParameters;
import org.apache.commons.configuration2.builder.BasicConfigurationBuilder;
import org.apache.commons.configuration2.builder.BuilderParameters;
import org.apache.commons.configuration2.builder.ConfigurationBuilderEvent;
import org.apache.commons.configuration2.builder.ConfigurationBuilderResultCreatedEvent;
import org.apache.commons.configuration2.builder.FileBasedConfigurationBuilder;
import org.apache.commons.configuration2.event.Event;
import org.apache.commons.configuration2.event.EventListener;
import org.apache.commons.configuration2.event.EventListenerList;
import org.apache.commons.configuration2.event.EventType;
import org.apache.commons.configuration2.ex.ConfigurationException;
import org.apache.commons.configuration2.interpol.ConfigurationInterpolator;
import org.apache.commons.configuration2.interpol.InterpolatorSpecification;
import org.apache.commons.lang3.concurrent.ConcurrentUtils;
/**
*
* A specialized {@code ConfigurationBuilder} implementation providing access to
* multiple file-based configurations based on a file name pattern.
*
*
* This builder class is initialized with a pattern string and a
* {@link ConfigurationInterpolator} object. Each time a configuration is
* requested, the pattern is evaluated against the
* {@code ConfigurationInterpolator} (so all variables are replaced by their
* current values). The resulting string is interpreted as a file name for a
* configuration file to be loaded. For example, providing a pattern of
* file:///opt/config/${product}/${client}/config.xml will result in
* product and client being resolved on every call. By storing
* configuration files in a corresponding directory structure, specialized
* configuration files associated with a specific product and client can be
* loaded. Thus an application can be made multi-tenant in a transparent way.
*
*
* This builder class keeps a map with configuration builders for configurations
* already loaded. The {@code getConfiguration()} method first evaluates the
* pattern string and checks whether a builder for the resulting file name is
* available. If yes, it is queried for its configuration. Otherwise, a new
* file-based configuration builder is created now and initialized.
*
*
* Configuration of an instance happens in the usual way for configuration
* builders. A {@link MultiFileBuilderParametersImpl} parameters object is
* expected which must contain a file name pattern string and a
* {@code ConfigurationInterpolator}. Other properties of this parameters object
* are used to initialize the builders for managed configurations.
*
*
* @since 2.0
* @param the concrete type of {@code Configuration} objects created by this
* builder
*/
public class MultiFileConfigurationBuilder
extends BasicConfigurationBuilder
{
/**
* Constant for the name of the key referencing the
* {@code ConfigurationInterpolator} in this builder's parameters.
*/
private static final String KEY_INTERPOLATOR = "interpolator";
/** A cache for already created managed builders. */
private final ConcurrentMap> managedBuilders =
new ConcurrentHashMap<>();
/** Stores the {@code ConfigurationInterpolator} object. */
private final AtomicReference interpolator =
new AtomicReference<>();
/**
* A flag for preventing reentrant access to managed builders on
* interpolation of the file name pattern.
*/
private final ThreadLocal inInterpolation =
new ThreadLocal<>();
/** A list for the event listeners to be passed to managed builders. */
private final EventListenerList configurationListeners = new EventListenerList();
/**
* A specialized event listener which gets registered at all managed
* builders. This listener just propagates notifications from managed
* builders to the listeners registered at this
* {@code MultiFileConfigurationBuilder}.
*/
private final EventListener managedBuilderDelegationListener =
new EventListener()
{
@Override
public void onEvent(final ConfigurationBuilderEvent event)
{
handleManagedBuilderEvent(event);
}
};
/**
* Creates a new instance of {@code MultiFileConfigurationBuilder} and sets
* initialization parameters and a flag whether initialization failures
* should be ignored.
*
* @param resCls the result configuration class
* @param params a map with initialization parameters
* @param allowFailOnInit a flag whether initialization errors should be
* ignored
* @throws IllegalArgumentException if the result class is null
*/
public MultiFileConfigurationBuilder(final Class resCls,
final Map params, final boolean allowFailOnInit)
{
super(resCls, params, allowFailOnInit);
}
/**
* Creates a new instance of {@code MultiFileConfigurationBuilder} and sets
* initialization parameters.
*
* @param resCls the result configuration class
* @param params a map with initialization parameters
* @throws IllegalArgumentException if the result class is null
*/
public MultiFileConfigurationBuilder(final Class resCls,
final Map params)
{
super(resCls, params);
}
/**
* Creates a new instance of {@code MultiFileConfigurationBuilder} without
* setting initialization parameters.
*
* @param resCls the result configuration class
* @throws IllegalArgumentException if the result class is null
*/
public MultiFileConfigurationBuilder(final Class resCls)
{
super(resCls);
}
/**
* {@inheritDoc} This method is overridden to adapt the return type.
*/
@Override
public MultiFileConfigurationBuilder configure(final BuilderParameters... params)
{
super.configure(params);
return this;
}
/**
* {@inheritDoc} This implementation evaluates the file name pattern using
* the configured {@code ConfigurationInterpolator}. If this file has
* already been loaded, the corresponding builder is accessed. Otherwise, a
* new builder is created for loading this configuration file.
*/
@Override
public T getConfiguration() throws ConfigurationException
{
return getManagedBuilder().getConfiguration();
}
/**
* Returns the managed {@code FileBasedConfigurationBuilder} for the current
* file name pattern. It is determined based on the evaluation of the file
* name pattern using the configured {@code ConfigurationInterpolator}. If
* this is the first access to this configuration file, the builder is
* created.
*
* @return the configuration builder for the configuration corresponding to
* the current evaluation of the file name pattern
* @throws ConfigurationException if the builder cannot be determined (e.g.
* due to missing initialization parameters)
*/
public FileBasedConfigurationBuilder getManagedBuilder()
throws ConfigurationException
{
final Map params = getParameters();
final MultiFileBuilderParametersImpl multiParams =
MultiFileBuilderParametersImpl.fromParameters(params, true);
if (multiParams.getFilePattern() == null)
{
throw new ConfigurationException("No file name pattern is set!");
}
final String fileName = fetchFileName(multiParams);
FileBasedConfigurationBuilder builder =
getManagedBuilders().get(fileName);
if (builder == null)
{
builder =
createInitializedManagedBuilder(fileName,
createManagedBuilderParameters(params, multiParams));
final FileBasedConfigurationBuilder newBuilder =
ConcurrentUtils.putIfAbsent(getManagedBuilders(), fileName,
builder);
if (newBuilder == builder)
{
initListeners(newBuilder);
}
else
{
builder = newBuilder;
}
}
return builder;
}
/**
* {@inheritDoc} This implementation ensures that the listener is also added
* to managed configuration builders if necessary. Listeners for the builder-related
* event types are excluded because otherwise they would be triggered by the
* internally used configuration builders.
*/
@Override
public synchronized void addEventListener(
final EventType eventType, final EventListener l)
{
super.addEventListener(eventType, l);
if (isEventTypeForManagedBuilders(eventType))
{
for (final FileBasedConfigurationBuilder b : getManagedBuilders()
.values())
{
b.addEventListener(eventType, l);
}
configurationListeners.addEventListener(eventType, l);
}
}
/**
* {@inheritDoc} This implementation ensures that the listener is also
* removed from managed configuration builders if necessary.
*/
@Override
public synchronized boolean removeEventListener(
final EventType eventType, final EventListener l)
{
final boolean result = super.removeEventListener(eventType, l);
if (isEventTypeForManagedBuilders(eventType))
{
for (final FileBasedConfigurationBuilder b : getManagedBuilders()
.values())
{
b.removeEventListener(eventType, l);
}
configurationListeners.removeEventListener(eventType, l);
}
return result;
}
/**
* {@inheritDoc} This implementation clears the cache with all managed
* builders.
*/
@Override
public synchronized void resetParameters()
{
for (final FileBasedConfigurationBuilder b : getManagedBuilders().values())
{
b.removeEventListener(ConfigurationBuilderEvent.ANY,
managedBuilderDelegationListener);
}
getManagedBuilders().clear();
interpolator.set(null);
super.resetParameters();
}
/**
* Returns the {@code ConfigurationInterpolator} used by this instance. This
* is the object used for evaluating the file name pattern. It is created on
* demand.
*
* @return the {@code ConfigurationInterpolator}
*/
protected ConfigurationInterpolator getInterpolator()
{
ConfigurationInterpolator result;
boolean done;
// This might create multiple instances under high load,
// however, always the same instance is returned.
do
{
result = interpolator.get();
if (result != null)
{
done = true;
}
else
{
result = createInterpolator();
done = interpolator.compareAndSet(null, result);
}
} while (!done);
return result;
}
/**
* Creates the {@code ConfigurationInterpolator} to be used by this
* instance. This method is called when a file name is to be constructed,
* but no current {@code ConfigurationInterpolator} instance is available.
* It obtains an instance from this builder's parameters. If no properties
* of the {@code ConfigurationInterpolator} are specified in the parameters,
* a default instance without lookups is returned (which is probably not
* very helpful).
*
* @return the {@code ConfigurationInterpolator} to be used
*/
protected ConfigurationInterpolator createInterpolator()
{
final InterpolatorSpecification spec =
BasicBuilderParameters
.fetchInterpolatorSpecification(getParameters());
return ConfigurationInterpolator.fromSpecification(spec);
}
/**
* Determines the file name of a configuration based on the file name
* pattern. This method is called on every access to this builder's
* configuration. It obtains the {@link ConfigurationInterpolator} from this
* builder's parameters and uses it to interpolate the file name pattern.
*
* @param multiParams the parameters object for this builder
* @return the name of the configuration file to be loaded
*/
protected String constructFileName(
final MultiFileBuilderParametersImpl multiParams)
{
final ConfigurationInterpolator ci = getInterpolator();
return String.valueOf(ci.interpolate(multiParams.getFilePattern()));
}
/**
* Creates a builder for a managed configuration. This method is called
* whenever a configuration for a file name is requested which has not yet
* been loaded. The passed in map with parameters is populated from this
* builder's configuration (i.e. the basic parameters plus the optional
* parameters for managed builders). This base implementation creates a
* standard builder for file-based configurations. Derived classes may
* override it to create special purpose builders.
*
* @param fileName the name of the file to be loaded
* @param params a map with initialization parameters for the new builder
* @return the newly created builder instance
* @throws ConfigurationException if an error occurs
*/
protected FileBasedConfigurationBuilder createManagedBuilder(
final String fileName, final Map params)
throws ConfigurationException
{
return new FileBasedConfigurationBuilder<>(getResultClass(), params,
isAllowFailOnInit());
}
/**
* Creates a fully initialized builder for a managed configuration. This
* method is called by {@code getConfiguration()} whenever a configuration
* file is requested which has not yet been loaded. This implementation
* delegates to {@code createManagedBuilder()} for actually creating the
* builder object. Then it sets the location to the configuration file.
*
* @param fileName the name of the file to be loaded
* @param params a map with initialization parameters for the new builder
* @return the newly created and initialized builder instance
* @throws ConfigurationException if an error occurs
*/
protected FileBasedConfigurationBuilder createInitializedManagedBuilder(
final String fileName, final Map params)
throws ConfigurationException
{
final FileBasedConfigurationBuilder managedBuilder =
createManagedBuilder(fileName, params);
managedBuilder.getFileHandler().setFileName(fileName);
return managedBuilder;
}
/**
* Returns the map with the managed builders created so far by this
* {@code MultiFileConfigurationBuilder}. This map is exposed to derived
* classes so they can access managed builders directly. However, derived
* classes are not expected to manipulate this map.
*
* @return the map with the managed builders
*/
protected ConcurrentMap> getManagedBuilders()
{
return managedBuilders;
}
/**
* Registers event listeners at the passed in newly created managed builder.
* This method registers a special {@code EventListener} which propagates
* builder events to listeners registered at this builder. In addition,
* {@code ConfigurationListener} and {@code ConfigurationErrorListener}
* objects are registered at the new builder.
*
* @param newBuilder the builder to be initialized
*/
private void initListeners(final FileBasedConfigurationBuilder newBuilder)
{
copyEventListeners(newBuilder, configurationListeners);
newBuilder.addEventListener(ConfigurationBuilderEvent.ANY,
managedBuilderDelegationListener);
}
/**
* Generates a file name for a managed builder based on the file name
* pattern. This method prevents infinite loops which could happen if the
* file name pattern cannot be resolved and the
* {@code ConfigurationInterpolator} used by this object causes a recursive
* lookup to this builder's configuration.
*
* @param multiParams the current builder parameters
* @return the file name for a managed builder
*/
private String fetchFileName(final MultiFileBuilderParametersImpl multiParams)
{
String fileName;
final Boolean reentrant = inInterpolation.get();
if (reentrant != null && reentrant.booleanValue())
{
fileName = multiParams.getFilePattern();
}
else
{
inInterpolation.set(Boolean.TRUE);
try
{
fileName = constructFileName(multiParams);
}
finally
{
inInterpolation.set(Boolean.FALSE);
}
}
return fileName;
}
/**
* Handles events received from managed configuration builders. This method
* creates a new event with a source pointing to this builder and propagates
* it to all registered listeners.
*
* @param event the event received from a managed builder
*/
private void handleManagedBuilderEvent(final ConfigurationBuilderEvent event)
{
if (ConfigurationBuilderEvent.RESET.equals(event.getEventType()))
{
resetResult();
}
else
{
fireBuilderEvent(createEventWithChangedSource(event));
}
}
/**
* Creates a new {@code ConfigurationBuilderEvent} based on the passed in
* event, but with the source changed to this builder. This method is called
* when an event was received from a managed builder. In this case, the
* event has to be passed to the builder listeners registered at this
* object, but with the correct source property.
*
* @param event the event received from a managed builder
* @return the event to be propagated
*/
private ConfigurationBuilderEvent createEventWithChangedSource(
final ConfigurationBuilderEvent event)
{
if (ConfigurationBuilderResultCreatedEvent.RESULT_CREATED.equals(event
.getEventType()))
{
return new ConfigurationBuilderResultCreatedEvent(this,
ConfigurationBuilderResultCreatedEvent.RESULT_CREATED,
((ConfigurationBuilderResultCreatedEvent) event)
.getConfiguration());
}
@SuppressWarnings("unchecked")
final
// This is safe due to the constructor of ConfigurationBuilderEvent
EventType type =
(EventType) event
.getEventType();
return new ConfigurationBuilderEvent(this, type);
}
/**
* Creates a map with parameters for a new managed configuration builder.
* This method merges the basic parameters set for this builder with the
* specific parameters object for managed builders (if provided).
*
* @param params the parameters of this builder
* @param multiParams the parameters object for this builder
* @return the parameters for a new managed builder
*/
private static Map createManagedBuilderParameters(
final Map params,
final MultiFileBuilderParametersImpl multiParams)
{
final Map newParams = new HashMap<>(params);
newParams.remove(KEY_INTERPOLATOR);
final BuilderParameters managedBuilderParameters =
multiParams.getManagedBuilderParameters();
if (managedBuilderParameters != null)
{
// clone parameters as they are applied to multiple builders
final BuilderParameters copy =
(BuilderParameters) ConfigurationUtils
.cloneIfPossible(managedBuilderParameters);
newParams.putAll(copy.getParameters());
}
return newParams;
}
/**
* Checks whether the given event type is of interest for the managed
* configuration builders. This method is called by the methods for managing
* event listeners to find out whether a listener should be passed to the
* managed builders, too.
*
* @param eventType the event type object
* @return a flag whether this event type is of interest for managed
* builders
*/
private static boolean isEventTypeForManagedBuilders(final EventType eventType)
{
return !EventType
.isInstanceOf(eventType, ConfigurationBuilderEvent.ANY);
}
}